1. Field of the Invention
The invention relates to an automatic transmission of a motor vehicle, and more particularly to an automatic transmission capable of establishing a plurality of gear stages or speeds by using a reduced number of clutches.
2. Description of Related Art
Automatic transmissions of motor vehicles, each including a plurality of planetary gear sets, clutches and brakes, have been widely used. Japanese laid-open Patent Publication No. 2000-199549 discloses an example of such an automatic transmission which is able to establish six forward gear stages or speeds by using three planetary gear sets, three clutches and two brakes.
However, each of the clutches used in the automatic transmission requires a drum, seal rings, a mechanism for canceling a centrifugal oil pressure in a cylinder chamber, and other components, for enabling the clutch to be rotated. Thus, the weight and cost of clutches are generally greater than those of brakes, and the use of clutches is also disadvantageous in terms of the axial length of the transmission.